The present invention relates to a propeller operating arrangement for vessels used in waterborne traffic, and in particular to a propeller operating arrangement which includes a propulsion unit which can be turned in relation to the hull of the vessel and, thus, also can be used for steering the vessel. The invention also relates to a method for moving and steering a vessel travelling in water.
Various ships or similar vessels (such as passenger ships and ferries, cargo vessels, lighters, oil tankers, ice-breakers, off-shore vessels, navy vessels etc.) are moved in most cases by means of the thrust or pulling force of a rotatable propeller or several propellers. Traditionally, vessels have been steered by means of separate rudder equipment.
Traditionally, propeller operating or rotation systems have been implemented in such a way that the drive device for the propeller shaft, such as a diesel, gas or electric engine, is positioned inside the hull of the vessel, from where the propeller shaft is led via a lead-through that has been sealed to render it watertight to outside the hull of the vessel. The propeller itself is situated at the other end, i.e., the end which extends outside the vessel, of the propeller shaft which is connected either directly to the engine or to a possible gearbox. This solution is employed in the majority of all vessels used in waterborne traffic in order to obtain the power required for moving them.
Later on vessels have been fitted with propeller units in which the direction of the thrust or pulling force produced by the propeller can be altered. In these, the equipment which creates the propulsion in the propeller shaft (ordinarily an electric engine) and a possible gearbox can be positioned outside the hull of the vessel inside a special chamber supported to turn in relation to the hull. According to another alternative, the propulsion is led by means of angle transmissions and drive shafts from the engine inside the hull of the vessel to inside the chamber supported to turn, which is outside the vessel (e.g., arrangements known as rudder propellers).
A propulsion unit fitted with an electric engine inside a chamber is disclosed in greater detail, e.g., in the applicant""s FI patent No. 76977. Units of this kind are generally referred to as azimuthing propulsion units, and, e.g., the applicant in this case supplies azimuthing units of this type under the trademark AZIPOD. A propulsion unit fitted with a drive engine outside the chamber is presented in, e.g., U.S. Pat. No. 3,452,703 (Becker).
This kind of propulsion unit fitted with a propeller external to the vessel can be turned in relation to the vessel, which means that it can also be used instead of a separate rudder device for steering the vessel. More precisely, the chamber containing the engine and/or gearbox and any required drive shafts is supported by means of a special pipe shaft or the like to turn in relation to the hull of the ship. The pipe shaft is taken through the bottom of the ship.
In addition to the benefits obtained through the omitting of the long propeller shaft and separate rudder device, the azimuthing propulsion unit in particular has been found to provide a fundamental improvement in the steerability of the vessel as well. The energy economy of the vessel has also been found to have been rendered more efficient. The use of azimuthing propulsion units in various vessels designed for waterborne traffic has indeed become more common in recent years, and it is assumed that their popularity will continue to grow.
In the known solutions, the turning arrangement of the propulsion unit has generally been implemented so that a gear rim or the like turning rim has been attached to the pipe shaft. constituting the unit""s turning shaft. This rim is rotated by means of hydraulic motors adapted to co-operate with the unit. The liquid pressure and flow required by the hydraulic motors is usually generated by means of pumps rotated by electric engines. The rotational motion of the rim is also halted and held in the halted position whenever no control movement is performed in the common solution by means of the same hydraulic motors. For this reason, there is constantly the operating pressure maintained by the pumps inside the hydraulic system, also when the vessel is driven straight ahead.
A hydraulic turning system is used, inter alia, since that hydraulics make it possible to produce the relatively large torque required for turning the propulsion unit at a relatively low speed of rotation at the same time as turning and steering the vessel by means of hydraulics can be controlled easily and relatively precisely with the aid of traditional valve machinery and similar hydraulic components. As was already mentioned earlier, one feature which have been obtained with a hydraulic system has been that such a system permits the turning movement of the propulsion unit""s shaft to be halted quickly and precisely at the desired position, and this position can then be held, something which has been regarded as an important feature as regards steering a vessel.
According to one known solution, four hydraulic motors have been positioned in connection with a turning rim. Correspondingly, the operating machinery which produces the hydraulic pressure required in the engines comprises four hydraulic pumps and the electric engines rotating them. The hydraulic motors are adapted to two separate hydraulic circuits in order to enhance the operating reliability of the turning equipment, so that both circuits have their own operating machinery which creates hydraulic pressure (a so-called tandem structure) Both circuits contain two pumps and two drive engines turning them, usually with an output of 125 kW, and so the system in its entirety comprises four 125 kW electric engines. This total output is sufficient to produce an adequate turning speed and torque for steering operations both at sea and in ports. In the open sea and at normal travelling speed, a greater torque is required and, at the same time, a turning speed of approx. 3.5 to 5.0 degrees a second (xc2x0/s) will usually suffice for the propulsion unit when sailing in open water. In ports, and in particular when sailing to the quay, a vessel""s manageability and xe2x80x9cagilityxe2x80x9d are more important features. Then a greater turning speed is required and, at the same time, the need for torque is not as great as when sailing in sea conditions and at higher speeds. For ports and other such steering situations, a speed of approx. 5.0 to 7.5 degrees a second is generally regarded as an adequate turning speed for a propulsion unit. In the known technology, the turning speed of the propulsion unit has been altered by altering the number of running pumps, i.e.,. by switching pumps on/off as required.
The reason why four 125 kW engines (two per circuit) are used in the vessels instead of two 250 kW engines (one per circuit) can be explained by safety considerations: in black-out situations the vessel""s emergency systems are able to feed sufficient power into 125 kW engines but would no longer be able to feed 250 kW engines, which would cause the vessel to become unsteerable.
In the known hydraulic solution, which has been found to be effective and dependable in itself, a number of drawbacks have, however, been detected. In order to obtain an adequate level of reliability and owing to the aforesaid dimensioning of the emergency systems, the vessels have to be fitted with an expensive and complicated hydraulics system consisting of several electric engines and hydraulic pumps and the components which these require (such as hydraulic pipes and valves, electric cables, control devices etc.). The installation of these, monitoring of their condition and maintenance call for a considerable amount of work. In the tandem system according to prior art, part of the benefit in efficiency of use of space and in the simplification of the hydraulics which has been obtained by means of an external propulsion unit, and an azimuthing propulsion unit in particular, is lost.
One drawback of the hydraulic systems is also the fact that they are known to have a tendency to leak/drip oil or similar hydraulic fluid into their surroundings, in particular from tubes and various connections and seal surfaces. This causes both a tidiness problem and also a safety risk. The internal pressure of the hydraulic system is also relatively high, and thereby the breakage of, e.g., a hydraulic tube can cause a major safety risk. When it is running, a hydraulic system is also noisy, and this has an effect, inter alia, on the working conditions of the operating personnel. The noise is continuous, since the system has to be switched on throughout the time when the vessel is in motion. In order to minimize these disadvantages, it should be possible to obtain a solution for reducing the number of hydraulic components and in particular various pipes, tubes and connections, and pumps and their operating engines.
Furthermore, in the known solution, the speed of the turning movement of the propulsion unit can be influenced only by altering the volume flow rate (the volume flow rate of the pumps) of the liquid pumped into the system, which is done either by altering the number of engines used and thereby of the pumps pumping the hydraulic fluid or the speed of revolutions of the engines. However, there are situations in which the possibility of a considerably wider range of turning speeds of the unit or even of a stepless turning speed would be desirable.
The purpose of the present invention is to eliminate the drawbacks of the known technology and to obtain a new, improved solution for turning a propulsion unit in relation to the hull of the vessel.
One objective of the invention is to obtain a solution in which the number of components in the hydraulic system can be reduced without compromising on turning speed, usability and the reliability of the system.
One objective of the invention is to obtain a solution whereby the overall economy of the propulsion unit""s hydraulic turning machinery is improved compared to the known solutions.
One objective of the invention is to obtain a solution by means of which the maximum power requirement of the turning machinery can be reduced.
One objective of the invention is to obtain a solution by means of which the noise level of the propulsion unit""s turning machinery can be reduced compared to the known solutions.
One objective of the invention is to obtain a solution by means of which the turning speed of the propulsion unit can be altered and/or controlled in a new way.
The present invention which obtains these objectives is based on the basic realization that the turning speed of the propulsion unit can be controlled by altering the rotational displacement of the hydraulic motors which turn the propulsion unit. More precisely, the arrangement according to the invention is characterized in particular by what is disclosed in the characterizing portion in enclosed independent claim 1.
The method according to the invention is characterized by what is disclosed in the characterizing portion in enclosed independent claim 7.
According to advantageous embodiments of the present invention, the means for altering the rotational displacement comprise a two-speed valve, a three-speed valve or the like valve fitted in connection with the hydraulic motor which valve can be used to alter the displacement of the motor, advantageously a radial piston motor. Said means for altering the displacement of the hydraulic motor can also be integrated into the hydraulic motor itself. According to an embodiment which is regarded as advantageous, the system comprises two hydraulic pumps and electric motor drives arranged to rotate them, and four hydraulic radial piston motors arranged so that their displacement can be altered, which motors have been arranged to rotate the turning rim arranged at the propulsion unit""s shaft means. The operating equipment of the hydraulic motor""s power input unit can include a frequency transformer. The adjustment of the turning speed of the propulsion unit""s shaft means can also be arranged to be stepless.
According to one embodiment which is regarded as advantageous, the displacement of the hydraulic motor is altered in a ratio of 2:3.
The turning speed of the shaft means can also be adjusted, in addition to altering the rotational displacement of the hydraulic motor, by adjusting the power input and/or volume flow rate of the pumps in the hydraulic system which operates the hydraulic motor.
The present invention provides a number of significant advantages. It allows the number of required components, such as pumps, their operating devices and hydraulic pipings and the connections between these to be reduced. The same maximum turning speed can be obtained with half of the electric power which is required in solutions according to prior art. The required amount of hydraulic medium can also be reduced. The pressure level of the system can also be reduced. The omitted components, smaller amount of medium and lower pressure level reduce the noise level of the system. The turning solution disclosed provides a propulsion unit turning arrangement that can be adjusted, in a versatile manner, with respect to the speed and which arrangement is implemented with fewer components and lower costs than before.
The invention and its other objects and advantages are described in greater detail in the following exemplifying disclosure with reference also to the enclosed drawing, where the corresponding reference numbers in the various Figures refer to corresponding features.